Biological Effects of Broadband Terahertz Pulses

Abstract

Recent progress in terahertz (THz) technology has resulted in the development of broadband, ultrafast laser-based THz pulse sources, as well as coherent, phase-sensitive THz detectors (Baxter and Guglietta 2011; Jepsen et al. 2011; Lee 2009; Mittleman 2013; Tonouchi 2007), and has spurred numerous applications of broadband, picosecond-duration THz pulses in medicine and biology. In particular, novel biomedical imaging modalities based on broadband THz pulses are showing much promise for improved noninvasive diagnosis of cancer (Ashworth et al. 2009; Fitzgerald et al. 2002; Woodward et al. 2003; Yu et al. 2012), assessment of burns (Arbab et al. 2011), and intraoperative tumor margin identi- cation (Ashworth et al. 2008). THz radiation is nonionizing, is sensitive to cellular water content, suers from signicantly less scattering in tissue than visible light, and can provide submillimeter imaging resolution (Siegel 2004; Zhang 2002). Imaging with broadband THz pulses, termed THz pulsed imaging, or TPI, oers important benets over continuous-wave, monochromatic THz imaging approaches (Pickwell-MacPherson and Wallace 2009). In addition to yielding structural images, it permits the collection of spectroscopic information within a broad spectral range, usually 0.1-3 THz, which in turn enables detection of variation in water content, ion concentrations, and other subtle dierences in the composition of biological samples (Masson et al. 2006; Zhang 2002). Many important biomolecules have unique conformation-state-dependent spectral ngerprints in the THz range (Cherkasova et al. 2009; Falconer and Markelz 2012; Fischer et al. 2002; Kim et al. 2008; Markelz et al. 2002), and much research is currently dedicated to identifying intrinsic THz spectroscopic biomarkers for label-free,13.1 Introduction ......................................................................................241 13.2 In Vitro Studies of Biological Eects of THz Pulses on Cells .....243